a mountain system located within Southern Siberia, in the south of Krasnoiarsk Krai, in Irkutsk Oblast, the western part of the Buriat ASSR, and the north-eastern part of the Tuva ASSR.
The Vostochnyi Saian begins on the left bank of the Enisei River, to the southwest of Krasnoiarsk, and stretches more than 1,000 km in a southeasterly direction almost to the shores of Lake Baikal.
Geological structure and minerals. In geological terms, the Vostochnyi Saian is an asymmetric folded structure with a northwestern orientation abutting the southwestern edge of the Siberian Platform. In terms of the age of the main folding, the Vostochnyi Saian is divided into two parts separated by a zone of deep faulting: the Late Precambrian (Riphean or Baikalian) in the northeast and the Early Caledonian (Cambrian) in the southwest. The structure of the northeastern part contains Precambrian rocks of varying age, such as ortho- and paragneisses, amphibolites, crystalline schists, green slates, marbles, and quartzites. Here a significant role is also played by intrusions of Upper Riphean granitoids and ultrabasites. The Precambrian rock forms a series of different-sized blocks separated by a system of deep and regional faults. The marginal blocks that abut the Siberian Platform are part of its highly uplifted fractured basement, which was involved in the zone of Baikalian folding. They are separated from the remaining portion of the Vostochnyi Saian by the so-called Main Fault, which in tectonic and metallogenetic respects is one of the most important structural parts of the Vostochnyi Saian.
The structure of the Early Caledonian part of the Vostochnyi Saian consists mainly of Lower Cambrian and partly of Middle Cambrian igneous-sedimentary formations and Lower Paleozoic granitoid intrusions. All these rocks form a series of major blocks that are separated by faults.
During the Devonian Period, on the Precambrian and Early Caledonian bases of the Vostochnyi Saian, depressions began to form (the Minusinsk, Rybinsk, and other depressions), and these were filled by igneous and gray-red sedimentary rocks of the Middle and Upper Paleozoic (from the Devonian to the Permian inclusively) and by intrusions of alkali granites and syenites of Devonian age. Beginning at this time as well as during almost the entire Mesozoic, the Vostochnyi Saian developed under continental conditions, and over most of the territory there occurred the destruction of the uplifted folded structure and a general leveling of the relief. In certain Mesozoic depressions, predominantly during the Middle Jurassic, terrigenous-carboniferous deposits of significant thickness were formed.
The chief minerals are mica (muscovite) occurring with Upper Riphean pegmatites; gold confined to the quartz, quartz-sulfide, and quartz-carbonate veins; graphite (Botogorskii Golets); Riphean ferruginous quartzites (Sosnovyi Baits); Late Precambrian bauxites; deposits of rare metals and rare earths occurring with Upper Riphean pegmatites, Middle Paleozoic alkali albitized granites, and carbonatites; asbestos occurring with ultrabasic rock; and phosphorites in the siliceous-carbonate rocks of the Early Caledonian part. In the southeast of the Vostochnyi Saian, chiefly in the Tunkinskaia Basin there are widely known mineral springs (in Arshan, Nilova Pustyn’, and other resorts).
N. S. ZAITSEV
Topography. The basic directions of the major ranges and chains in the Vostochnyi Saian coincide with the strike of the main tectonic structures and major faults. The general protracted leveling of the terrain of the Vostochnyi Saian was interrupted in the Neocene by domelike uplifts that were accompanied by differentiated movements of individual blocks. The intensification of these movements, which at the end of the Neocene and in the Anthropogene Period created the present mountainous appearance of the Vostochnyi Saian, was accompanied in the eastern portion of the system by the abundant eruption of basaltic lavas, by ubiquitous intensive erosion, and by repeated glaciation of the most uplifted areas—-glaciations that had a mountain-valley and in places a semimantle character.
In the western part of the Vostochnyi Saian, flat-topped ranges predominate, which, as they gradually rise in a southeasterly direction, form the so-called belogor’ia (white mountains)—such as the Mana Belogor’e and the Kan Belogor’e—and the belki, which were named thus because of the patches of snow that remain on them for a larger portion of the year.
In the upper reaches of the Kizir and Kazyr rivers are located the Agul Belki, which, along with the adjoining Kryzhina Range on the west and the Ergak-Targak-Taiga (Tazarama) Range, which approaches from the south and is part of the Zapadnyi Saian, form the largest alpine plexus of the Vostochnyi Saian, with elevations almost up to 3,000 m and clearly expressed alpine landforms. From this same plexus runs the dividing Uda Range, which is an alpine chain with a very rugged relief. Further to the southeast, the dividing ranges of the Vostochnyi Saian assume the character of flat-peaked massifs, but to the east of the Tissa River, alpine crests again predominate (the Bol’shoi Saian Range), reaching the greatest elevation for the entire Vostochnyi Saian in the mountain group Munku-Sardyk (3,491 m). To the north of Munku-Sardyk, stretch the high Kitoi and Tunkinskie Gol’tsy, which are parallel to each other and run east to west and which are separated from the main ranges of the Vostochnyi Saian along the right bank of the Irkut River by a system of intermontane depressions (such as Tunkinskaia Basin).
Along with the rugged landforms, the Vostochnyi Saian is also characterized by extensive areas of ancient leveled relief, lying usually at altitudes of from 1,800-2,000 m to 2,400-2,500 m; in the eastern part, in the interfluve of the Khamsara and Bol’shoi Enisei and in the basin of the upper course of the Oka River, the topography also consists of gently sloping plateaus composed of tuffs and lavas that had erupted from the large shield volcanoes. In contrast to these volcanoes, which at present have already been significantly destroyed by denudation, the Vostochnyi Saian (the Oka River basin) also has well-preserved, very young volcanic formations (the Kropotkin, Peretolchin, and other volcanoes).
For most of the slopes of the mountain ranges located at an altitude below 2,000 m, a typical mid-mountain relief is characteristic, with deeply incised valleys and relative elevations up to 1,000-1,500 m. Below, the complex of these forms is girdled by the hilly and low-mountain relief of the foothills.
In the intermontane basins (such as Tunkinskaia) as well as in the lower courses of the Kazyr and Kizir rivers, various types of aggradation relief have developed formed by glacial, glaciofluvial, and lacustrine deposits (an undulating-morainic relief, terminal moraines, kame terraces, and so forth).
Climate. The climate is sharply continental, with prolonged and severe winters and cool summers with variable weather, and with the bulk of the precipitation occurring during the summer. The continental character of the climate intensifies from west to east. At altitudes of 900-1,300 m the mean January temperature varies from -17° to -25° C; and in July, from 12° to 14° C. The distribution of precipitation is closely dependent upon the exposure of the mountain slopes. On the western and southwestern slopes, which are exposed to wet air currents, precipitation is up to 800 mm or more per year; in the northern foothills, up to 400 mm; and in the eastern and southeastern regions, which are in the “rain shadow,” not more than 300 mm. In the west there is a great deal of snow during the winter, while in the east there is little. Series of permafrost rock are widely found in the east. In the highest massifs—such as the eastern part of the Kryzhina Range, the region near Topografov Peak (the largest center), and Munku-Sardyk—there are modern, predominantly cirque glaciers. Around 100 small glaciers with a total area of about 30 sq km are known.
Rivers and lakes. The river network of the Vostochnyi Saian belongs to the Enisei Basin. The major rivers are the Tuba (with the Kazyr and Kizir), Syda, Sisim, Mana, Kan with the Agul, Biriusa with the Tagul, and the tributaries of the Angara—the Uda (Chuna), Oka (with the lia River), Belaia, Kitoi, and Irkut; the Bol’shoi Enisei (Bii-Khem) and its right tributaries (the most important are the Bash-Khem, Tora-Khem with the Azas, and Khamsara) rise from the southern slopes. A majority of the rivers have a mountainous character over virtually their entire length, and only the rivers that rise within areas of the leveled terrain flow in the headwaters through broad, flat valleys. The rivers are fed primarily by snow and rain. They open up at the end of April and the beginning of May and freeze over at the end of October and November. All the large rivers possess great reserves of hydroelectric power, and many of them are used for floating timber. On the Enisei, where the river cuts through the spurs of the Vostochnyi Saian (close to the Divnye Mountains), the Krasnoiarsk Hydroelectric Power Plant has been built.
A majority of the area’s lakes are of glacial origin. The most important lakes are Agul’skoe, which lies in a tectonic depression at an altitude of 992 m, and the ponded morainic lakes of Tiberkul’ and Mozharskoe, which are located at an altitude of about 400-500 m.
Types of landscapes. The basic types of landscapes in the Vostochnyi Saian are mountain-taiga and alpine. Only in the foothills (elevations up to 800-1,000 m) and in the Tunkinskaia Basin is there a predominance of light larch and pine forests alternating with forest-steppe and meadow-swamp areas (along the valley of the Irkut River).
The typical mountain-taiga landscapes, which occupy more than 50 percent of the area of the Vostochnyi Saian, have developed on the slopes of all the main ranges and in the river valleys. The mountain-taiga zone is characterized by a moderately cool and sufficiently wet climate (particularly in the west). In the western and central areas, on soils of the mountain taiga type that are slightly podzolic, light, and deeply leached, there is a predominance of dark coniferous taiga forests of spruce, cedar, and fir, rising up to an altitude of 1,500-1,800 m; in the east and southeast, on soils of the mountain permafrost-taiga type that are humus-podzolized, as well as on acid soils having iron accumulation, there are lighter larch-cedar forests forming a timberline at an altitude of 2,000-2,250 m.
The mountain-taiga forests are the basic habitat for the most important representatives of the animal world, many of which are hunted. Here dwell the squirrel, hare, fox, roe deer, maral, elk, brown bear, and other animals; of the birds there are the hazel hen, capercaillie, woodpeckers, nutcrackers, and others. Sable and musk deer are found along the upper edge of the forest and among the rocks.
The alpine landscapes are noted for their severe climate, long and cold winters, short and cool summers, and intensely occurring processes of solifluction and physical weathering. On the leveled divides there is a predominance of brush and moss-lichen stony tundra on shallow mountain-tundra soils; in the western, wetter portion of the Vostochnyi Saian, along with the mountain tundra, subalpine brush and meadows are often found, and in places there are high-grass meadows. The rugged slopes and peaks of the alpine-type mountains are a stony desert almost devoid of vegetation. Stone debris and rock streams have developed widely.
Within the alpine area, the reindeer is encountered; pikas, the alpine ptarmigan, and the willow grouse are common.
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I. G. NORDEGA